Plant cells and tissues can respond to mechanical, chemical or pathogen induced injury by producing various phenolic compounds including mono- or dimethoxylated lignin precursors derived from cinnamic acid via a complex series of biochemical reactions. These lignin precursors are eventually used by the plant to produce the phenolic macromolecule lignin which helps in wound repair by adding hydrophobicity, a physical barrier against pathogen infection and mechanical strength to the injured tissue (Vance, C. P., et al., 1980, Annu Rev Phytopathol 18:259-288).
Cinnamyl-alcohol dehydrogenase (CAD) catalyzes the final step in the production of lignin monomers and has been implicated in plant defense response to fungal infection. Because of lignins importance in cell wall architecture and wound repair mechanisms there is considerable interest in the prospects for altering lignin quantity or quality by genetic engineering. For example, chemical treatments needed to remove lignin during the paper-pulping process are expensive and environmentally unfriendly. Plants with altered lignin quantity or quality could benefit this industry (Boudet, A., et al., 1996, Mol Breeding 2:25-39; Campbell, M., et al., 1996, Plant Physiol 110:3-13). Also, during soybean seed storage and processing lignin monomers are often oxidized, via polyphenol oxidase, to compounds that impart an undesirable yellow color to soybean seeds and seed products. It may be possible to reduce the amount of these phenolic compounds by suppressing CAD activity.
Cinnamyl-alcohol dehydrogenase genes described herein appear to be part of a multigene family. This application details the discovery of several different CAD genes from rice, soybean and wheat. Based on homology each of the genes (which range from 24% to 82% in similarity) have been placed into one of five different sub-groups that make up the CAD multigene family. There is a great deal of interest in identifying the genes that encode proteins involved in the production of lignin in plants. These genes may be used in plant cells to control lignin production. Accordingly, the availability of nucleic acid sequences encoding all or a portion of an enzyme involved in the production of lignin would facilitate studies to better understand lignin production in plants and provide genetic tools to enhance or otherwise alter lignin biosynthesis which in turn could provide mechanisms to control cell wall architecture, host defense and injury repair mechanisms and reduce the pool of phenolic compounds in plant cells.